1. Field of the Invention
The present invention concerns a method for fabricating ultra-thin electrical interconnection cables having a plurality of individually conducting lines disposed between two layers of insulating material.
2. Description of the Background Art
Numerous types of advanced electronics and electrooptical devices frequently require a large number of electrically conducting interconnections between various internal components such as large scale integrated circuits. These interconnections are frequently accomplished using thin ribbons containing a plurality of thin conducting lines disposed in spaced apart relation between two layers of insulating material. Conducting ribbons of this type commonly have as many as 50 separate conducting lines and are generally referred to as flex cables.
In certain applications, such as those involving cryogenic temperatures or where a large number of photosensitive detectors are densely located within a small focal area, the flex cables employed must be very flexible to facilitate connection to extremely small electronic components and very thin to minimize thermal conductivity and thereby minimize loss of cryogenic coolant.
Very thin flex cables have previously been fabricated by attaching a ribbon of conductive metallic foil to a base layer of polyimide tape such as KAPTON (a trademark of DuPont) coated with a layer of suitable adhesive, etching the thin metallic foil by standard photolithographic processes to form a plurality of separate conducting lines, and then laminating the resulting spaced apart conducting lines with a second layer of polyimide tape, again coated with a suitable adhesive. Flex cables having a minimum thickness of about 0.0023 inches (0.006 cm) have been fabricated using the above methodology even when extremely thin adhesive-backed polyimide tapes are used.
Another method of fabricating thin flex cables is disclosed in U.S. Pat. No. 3,525,652 in which a thin metallic ribbon is repeatly dipped in a liquid polyimide or similar insulation bath to produce a flex cable having a single broad conducting path and a minimum thickness of about 0.0028 inches (0.007 cm).
There still exists a need for thinner flex cables having improved flexibility and even lower thermal conductivity. Therefore, one object of the present invention is to provide a method of fabricating ultra-thin flex cables of improved flexibility and lower thermal conductivity.